The invention relates to surge protection circuitry. More particularly, the invention relates to methods and systems for reducing clamp voltages in surge protection circuitry.
Electrical power surges can cause equipment failure. Surges can be transient in nature, and may be caused by events such as lightning strikes, short-circuited power lines, or power supply failure. Equipment failure results from failure of electrical circuits that are unable to handle high energy signals.
Transient, or surge protection devices protect equipment from failure by providing a path to ground for high energy signals, so that the high energy signals bypass downstream equipment. A common method of implementing a surge protection device is to provide a low resistance path to ground which is usually disconnected from downstream equipment to be protected but becomes connected to the downstream equipment when a high energy signal is sensed.
Conventional surge protection devices may include a suppression component such as a diode, coupled between a power supply and downstream equipment that is to be protected by a surge protection device. When the diode senses a high-energy electrical signal and if the voltage of the signal is above the threshold voltage, the diode starts conducting current to ground. The magnitude of voltage at which the signal causes the diode to conduct is called the clamp voltage and is equal to the sum of the threshold voltage of the diode and any voltage drop caused by impedance in any electrical connection of the diode. Ideally, the clamp voltage should be close to the diode threshold voltage because diode threshold voltages are generally well specified under a range of operating conditions, unlike electrical connection impedances. Impedance is unpredictable with respect to transient high energy signals because it is proportional to voltage switching frequencies which are unpredictable.
Surge protection devices are often implemented on printed circuit boards in order to minimize the size of the device, to automate production, and to reduce the cost of production. Printed circuit boards typically may include an insulating substrate to isolate components mounted thereon and copper traces on the substrate to connect components (e.g., integrated circuits). The copper traces connecting the components generate inductance when the traces conduct current. Typically, power supply signals to equipment, and to electrical circuits in general, is either of zero frequencyxe2x80x94i.e., DC (Direct Current)xe2x80x94or of a fixed non-zero frequencyxe2x80x94i.e., AC (Alternating Current)xe2x80x94. Therefore, when the suppression components in a surge protection device are not conducting current, the copper traces generate inductive reactances of small or zero magnitude.
However, during transient conditions, the electrical signals presented to surge protection devices are typically of higher frequencies. At higher frequencies, the trace inductance of the printed circuit board forms a larger portion of trace impedance, as impedance, Z, of an inductor is described by Z=jxcfx89L (frequency, xcfx89; inductance, L). Therefore, it is desirable to reduce trace inductances, thereby decreasing clamp voltages of surge protection devices.
A typical surge protection device may include diodes connected in parallel that conduct in the event that high energy signals occur. In an effort to reduce the size of the overall surge protection device, more than one diode is often required to meet the specifications for the surge protection device. In a typical arrangement of parallel-connected diodes, electrical connections can contribute both self-inductance and mutual inductance to trace inductances.
Therefore, it is desirable to provide a method for connecting suppression components in surge protection devices such that the clamp voltages of the surge protection devices are reduced.
It is an object of the invention to provide a method for connecting suppression components in surge protection devices such that the clamp voltages of the surge protection devices are reduced. If overall inductance in a surge protection device is decreased, the clamp voltage of the surge protection device is reduced. The present invention provides a method for arranging suppression components such that overall inductance is decreased, by decreasing mutual inductance. The orientation of suppression components can be manipulated such that when the suppression components conduct, the current flow of neighboring suppression components can be in opposite directions. The direction of current flow affects the direction of any magnetic field induced by the current flow, and hence any mutual inductance caused by the current flow. Additive effects of mutual inductance may thus be reduced by changing the orientation of the suppression components. A reduction in overall inductance follows any reduction in mutual inductance, and thus, a method is provided for decreasing the clamp voltage of a surge protection device.